What's the process to untether after tethered?

I'm short on time (having a baby this week) and I wanted to get up to date with the latest fw while I still have some free time. Since I don't have a Mac and don't want to deal w/ the bugs in this current redsn0w... I have some tethered questions:

1. Can you re-spring a tethered jb without going through the tether-reset?
2. When (and if) comex's untether for 4.2.1 comes out, would I need to redo everything? Or would it be a "patch" of some sort?

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